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Difficulty: MediumCreate and Configure Virtual Networks and Subnets

Your company has an Azure environment with a virtual network named `vnet-hybrid-prod` that has an address space of 10.150.0.0/2210.150.0.0/22. The virtual network contains an existing subnet named `snet-db` with an address range of 10.150.0.0/2410.150.0.0/24.

You plan to deploy a VPN Gateway and a new application cluster to `vnet-hybrid-prod`. You must satisfy the following requirements:
- The VPN Gateway must be deployed to a subnet named `GatewaySubnet`.
- The application cluster will consist of 27 virtual machines that require individual private IP addresses.
- You must minimize IP address waste.

Which two subnets should you create to meet the requirements? (Choose two.)

  1. snet-application with the address range 10.150.2.0/2710.150.2.0/27Answer
  2. GatewaySubnet with the address range 10.150.1.0/2710.150.1.0/27Answer
  3. C
    snet-application with the address range 10.150.0.128/2710.150.0.128/27
  4. D
    snet-application with the address range 10.150.3.0/2810.150.3.0/28
  5. E
    GatewaySubnet with the address range 10.150.1.0/3010.150.1.0/30

Answer

The correct subnets are 'snet-application with the address range 10.150.2.0/2710.150.2.0/27' and 'GatewaySubnet with the address range 10.150.1.0/2710.150.1.0/27'.
To host 27 virtual machines, a subnet must support at least 27 usable IP addresses. Since Azure reserves 5 IP addresses per subnet, the total addresses needed is 27+5=3227 + 5 = 32, which corresponds to a /27 prefix. The option with 'snet-application with the address range 10.150.2.0/2710.150.2.0/27' satisfies this without overlapping with the existing subnet. Furthermore, the option with 'GatewaySubnet with the address range 10.150.1.0/2710.150.1.0/27' is correct because Azure requires the GatewaySubnet to use a prefix size of /29 or larger, and it does not overlap with the other subnets.

Step-by-Step Solution

1
Calculate the subnet size required for the 27 virtual machines.
A /27 subnet size is required.
A subnet of size /28 provides 16 IP addresses. Subtracting the 5 Azure-reserved IP addresses leaves only 11 usable IPs, which is insufficient. A subnet of size /27 provides 32 IP addresses; subtracting the 5 reserved IPs leaves exactly 27 usable IP addresses, satisfying the requirement with zero wasted host IPs.
2
Verify that the proposed application subnet does not overlap with existing subnets.
The range 10.150.2.0/2710.150.2.0/27 is valid and non-overlapping.
The existing subnet `snet-db` occupies 10.150.0.0/2410.150.0.0/24 (10.150.0.010.150.0.0 to 10.150.0.25510.150.0.255). The subnet `snet-application` with the range 10.150.2.0/2710.150.2.0/27 (10.150.2.010.150.2.0 to 10.150.2.3110.150.2.31) does not overlap with `snet-db`.
3
Select a valid size and range for the GatewaySubnet.
The range 10.150.1.0/2710.150.1.0/27 is valid.
Azure GatewaySubnet requires a prefix size of /29 or larger (e.g. /28, /27). A /30 prefix is invalid and will fail deployment. The range 10.150.1.0/2710.150.1.0/27 does not overlap with `snet-db` (10.150.0.0/2410.150.0.0/24) or the newly proposed `snet-application` (10.150.2.0/2710.150.2.0/27).

Key Concept

Determining Azure subnet sizes based on usable host requirements (accounting for the 5 reserved IP addresses) and satisfying specialized subnet constraints (such as GatewaySubnet size limits) without IP overlaps.
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Topics

Create and Configure Virtual Networks and Subnets